(1) Field of the Invention
The present invention relates to a tracking control device for a magnetic recording/reproducing apparatus for recording/reproducing information along a plurality of tracks running in parallel to the direction in which a magnetic tape moves by successively moving magnetic heads in the widthwise direction of the magnetic tape.
(2) Description of the Related Art
A magnetic recording/reproducing device for use in an audio apparatus has been usually arranged in such a manner that the number of the tracks and that of the heads are the same except for devices having a rotary head. The "number of the tracks" means the total number of data tracks formed in parallel to a direction in which the tape moves. The "number of heads" means the number of magnetic heads included by a combination head which integrally has magnetic heads such as the recording heads and reproducing heads or the recording/reproducing heads. A magnetic recording/reproducing apparatus of the type described above is provided with tape head relative position restricting means for restricting the relative position between the magnetic tape and the magnetic head. A typical restricting means has a guide post in which there is formed a pair of flanges for guiding the two widthwise directional ends of the magnetic tape.
The above-described tape head relative position restricting means is arranged to prevent the vertical waving of the magnetic tape by bringing the two ends of the magnetic tape into contact with the flanges. However, when a magnetic tape is wider than the distance between the two flanges, the ends of the magnetic tape can be damaged due to mechanical stress applied to the ends of the magnetic tape. Since the magnetic tape must be protected from damage, it has been difficult to improve the accuracy in positioning the magnetic tape more precisely than within several tens of micromillimeters. What is even worse, the above-described problem experienced with a high density magnetic recording/reproducing apparatus the allowable offtrack quantity of which is in a range between a level of ten and several tens of millimeters cannot satisfactorily be overcome by simply restricting the positional movement of the magnetic tape by the above-described flanges.
Recently, thin film magnetic heads have been advanced, causing combination heads of a type having a large number of heads to be developed. Therefore, the degree of density in the multi-track magnetic recording/reproducing apparatus can further be raised. The apparatus of the type described above is able to record data to a track having a narrower width. However, the allowable offtrack is reduced. Therefore, an apparatus of the type described above have a tape head relative position restricting means arranged to comprise, in addition to the above-described flanges, control means for causing the magnetic head to follow waving of the magnetic tape by its means for detecting the relative position between the magnetic head and the magnetic tape or between the magnetic head and a track, and head drive means for moving the magnetic head in the widthwise direction of the tape.
The above-described apparatus is exemplified by a fixed head digital audio tape recorder arranged in such a manner that the number of the heads and that of the tracks are the same.
The above-described apparatus is, as disclosed in Singaku Giho EA83-56, Shingaku Giho EA81-64 and Sharp Giho 1984-28, arranged in such a manner that a servo only track recorded on a magnetic tape is traced by a pair of reproducing heads disposed in parallel to each other in the widthwise direction of the tape. The thus obtained reproduced outputs are subjected to a comparison so that a following control is performed. As a result, the relative position between the magnetic head and the magnetic tape is restricted.
As another example of the tape head relative position restricting means, a control device of a magnetic recording/reproducing apparatus which is arranged in such a manner that the number of the heads and that of the tracks are the same has been disclosed (Japanese Patent Publication No. 63-64811). The control device is arranged in such a manner that a tracking signal is recorded along an end of the magnetic tape in the widthwise direction. The tracking signal thus recorded is reproduced by a servo reproducing head so as to subject the reproduced signal level to a comparison with a reference level. As an alternative to this, tracking information is recorded along the two ends of the magnetic tape in the widthwise direction. The thus recorded tracking information is reproduced by a pair of servo reproducing heads. The levels of the two reproduced signals are subjected to a comparison with each other. As a result, the tracking is performed.
Since the multi-track magnetic recording/reproducing apparatus such as the above-described fixed head digital audio tape recorder has a track pitch of hundreds of micromillimeters, a combination head in which a plurality of recording heads and reproducing heads are integrally formed can be used by employing a thin film head. The plurality of recording heads and the reproducing heads correspond to a plurality of tracks formed on the magnetic tape.
To raise the recording density, the track width can be reduced by reducing the gap width of the magnetic head. However, since the degree of integration of the thin film head involves a certain limitation, the track pitch cannot be reduced satisfactorily. What is even worse, when the number of the heads is increased, the size of the circuit will be enlarged, causing an excessive cost to be raised. Therefore, a high density magnetic recording/reproducing apparatus which is arranged in such a manner that the track pitch is several tens of micromillimeters and the number of the tracks is several tens to hundreds cannot be realized by a structure in which the number of the heads and the number of the tracks are the same.
Accordingly, a recording system called a serpentine system has recently been employed in a multi-track magnetic recording/reproducing apparatus which is a backup storage device for an information processing system and which is usually called a cassette streamer. The serpentine system being arranged in such a manner that the number of the heads is smaller than the number of the recording heads.
The serpentine system will be described with reference to FIG. 1. A magnetic tape 21 which moves in direction X and the width of which is designated by Y has a track group 22 composed of 16 tracks T1 to T16 which are, for example, formed in direction Y at equal pitch a. A combination head 23 is disposed to correspond to the above-described track group 22, the combination head 23 comprising, for example, four recording heads W1 to W4 and four reproducing heads R1 to R4.
The recording heads W1 to W4 are disposed in the direction Y at same pitch b (b=4a), each of the reproducing heads R1 to R4 being arranged to form a pair in cooperation with corresponding recording heads W1 to W4 disposed in direction X or -X.
When the recording or reproducing operation is performed, the above-described combination head 23 is first moved to a position shown in FIG. 1. That is, it is moved to a position at which the center of the recording head W1 and that of the reproducing head R1 coincide with the center of the track T1, the center of the recording head W2 and that of the reproducing head R2 coincide with the center of the track T5, the center of the recording head W3 and that of the reproducing head R3 coincide with the center of the track T9 and the center of the recording head W4 and that of the reproducing head R4 coincide with the center of the track T13.
In this state, the magnetic tape 21 is moved in the direction X when data is recorded so that data is simultaneously recorded to the tracks T1 and T9 by the recording heads W1 and W3.
After data recording to a lengthwise end of the magnetic tape 21 has been ended, the magnetic tape 21 is moved in the direction -X so that data is simultaneously recorded to the tracks T5 and T13 by the recording heads W2 and W4. After data recording to a lengthwise end of the magnetic tape 21 has been ended, the combination head 23 is moved in the direction -Y by the track pitch a so that the center of the recording head W1 and that of the reproducing head R1 are made coincide with the center of the track T2. Then, the magnetic tape is allowed to reciprocate in the directions X and -X while maintaining the thus realized relative position. As a result, data is recorded to the tracks T2, T6, T10 and T14. Then, the combination head 23 is similarly moved by a in the direction -Y whenever the magnetic tape 21 reciprocates once. Thus, information is recorded to all of tracks T1 to T16 after four times of the reciprocating motions have been completed.
The above-described serpentine system multi-track magnetic recording/reproducing apparatus is constituted in such a manner that data is recorded/reproduced from a multiplicity of tracks by moving a reduced number of magnetic heads in the widthwise direction of the tape. Therefore, the track pitch can be reduced and the number of the tracks can thereby be increased by arranging the structure in which the magnetic head is moved by a multiplicity of times. Therefore, the thin film head can be integrated smoothly.
As the head tape relative position restricting means of the serpentine system multi-track magnetic recording/reproducing apparatus, a head positioning technology has, as disclosed in, for example, Japanese Patent Laid-Open No. 62-183019, been known in which the stepping motor is open-loop-controlled in addition to the restriction performed by the above-described flanges.
However, in the serpentine system magnetic recording/reproducing apparatus in which the track pitch is several tens of micromillimeters, the track width becomes, of course, several tens of micromillimeters. Therefore, the offtrack becomes a level of ten to several micromillimeters. However, the tape head relative position restricting means arranged in such a manner that the above-described open-loop control is performed cannot correspond to the small above-described allowable offtrack.
In a case where the total stroke of the combination head of the above-described serpentine system magnetic recording/reproducing apparatus is about 1 mm at the time of switching the track, the servo reproducing head must have a relatively large dynamic range of about 60 dB in order to reduce the tracking residual error to be smaller than 1 .mu.m.
However, the conventional method in which one servo track is traced by two servo heads encounters a problem in that satisfactory S/N ratio and linearity cannot be obtained in overall region of the large dynamic range. Therefore, the tracking accuracy at each track switch position has been unsatisfactory.